The properties view only creates the list of selectable property lists once when created. Changing the (amount of) windows afterwards (like closing the Std MultiWidget and opening the MxN MultiWidget instead) can create crashes when trying to access windows (or rather, renderers) that no longer exist.
This list should be updated any time the windows change.

Steps to reproduce:

• open MITK workbench
• open properties view
• open MxN Multi Widget
• close the Std Multi Widget
• select one of the windows in the properties view (e.g. Data node: stdmulti.widget0)

-> crash